Specifically, in Egypt, several studies have been carried out to study the effect of environmental conditions and climate changes on archaeological sites. For instance, in the Giza pyramid area, Emery [13] studied the weathering conditions on the Great Pyramid and revealed four types of limestone used to build it, such as gray hard dense limestone, soft gray limestone, gray shaly limestone, and yellow limy shaly sandstone. Furthermore, Hanafy and Holail [14] presented a diagnosis study of the middle Eocene "nummulite bank" of the Giza Pyramid Plateau and explained that the early diagenetic alteration of the rock matrix was followed by partial to complete dolomitization of the limestone matrix and nummulite grain. Reader [15] studied the weathering problems and erosion on Sphinx and presented a geomorphological study for Giza Necropolis. USAID of Egypt [16] presented an assessment report to study the environmental impacts on the Giza plateau and suggested a methodology for groundwater lowering. In addition, Gandah [17] studied and discussed the environmental impacts of rain, wind, and salts on the pyramid of Khufu and presented hypotheses for restoration and conservation. Zalewski [18] studied and gave us the opportunity to see the construction materials of the Great pyramid in his study through the petrography observations of the building stones. Finally, Hemeda and Sombol [19] studied and discussed the durability problems of the Great pyramids and the effect of subsurface and underground water on the stability of the pyramid.
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In Saqqara necropolis, Madkour and Khallaf [20] explained the degrading process of the faience inside the step pyramid, and the results showed that salt crystallization from the wall support (Bedrock) was the main problem that generally affected the faience and the substructure of the pyramid. Kukela [21] studied the degradation patterns for the Step pyramid of Saqqara and showed isometric deterioration maps for the pyramid. Furthermore, Khalil et al. [22] showed the effects of strong ground shaking on the stability of the Step pyramid and showed that there are many earthquakes in Greater Cairo with low magnitudes but with accumulative effects for the long term on the pyramid. Additionally, Rossi [23] utilized the advanced digital documentation method to monitor the area of the New Kingdom in Saqqara and showed the effect of wind, humidity, and temperature on the archaeological building. Finally, Ahmed [24] described the deterioration patterns for all faces of the Step pyramid and showed the geoenvironmental challenges, such as earthquakes, over the Step pyramid. In Dahshour necropolis, Hemeda et al. [25] studied the geoenvironmental impacts and structural problems on the northern pyramid of Snefru at the archaeological site. Often, there are no more studies that investigate the geoenvironmental problems and material characterizations at the Dahshour and Abusir archaeological sites. Accordingly, the present study is a significant study to investigate the durability and environmental problems of the construction materials of Sahure's pyramid at the Abusir archaeological site.
Abusir is a sophisticated archaeological site with different kinds of building materials and pyramids. The preservation state of this site is extremely poor and forgotten. Sahure's pyramid has been affected by damage from various geoenvironmental impacts. In this sense, the durability and resistance of the pyramid decreased physically and mechanically (Fig. 1c and d). For all these motives, the main aims of this paper are (1) to identify the geological and meteorological conditions related to this site; (2) to characterize the construction materials of Sahure's pyramid by means of geochemical, petrographical, and petrophysical approaches; (3) to evaluate the durability and vulnerability of the ancient construction materials of the pyramid; and (4) to present a proposal for scientific conservation and protection of the pyramid. To achieve all these aims, this study has carried out a hazard analysis for the construction materials of the pyramid utilizing different analytical and examination techniques of X-ray diffraction, X-ray fluorescence, and optical microscopy. In addition, the physical properties of the core building material of the pyramid are determined to confirm the environmental impacts on the physical properties of the construction materials used.
a Cross section and b Plan of the Sahure pyramid. The colors in cross-section represent the white fossiliferous limestone from the Tura quarry (casing stone, in white); the body of the pyramid made by laminated sandy argillaceous limestone (marl, in white gray); granite (casing for entrance and some parts in the corridor, in red); and bedrock from limestone (in dark gray). Edited after Ref. [35]
Generally, the Memphis area consists of different geological features, such as Nile silts, which are located on the eastern and western sides of the Nile River and adjacent to the archaeological sites in Memphis, Wadi (Valley). In addition, deposits include neonile deposits, pronile deposits, undifferentiated pronile deposits, limestone intercalated with shale stones, and Cretaceous formations [38] (Fig. 3a). Specifically, Abusir geological formations are considered from the Late Eocene, and Maadi limestone, clay-limestone, and marls crop out (tafla) (Fig. 3a and b). The upper member of the Maadi Formation (blue legend, Fig. 3b), which is connected to the Abusir area, is developed mostly as porous brown sandy limestone in-tempestite facies [38]. According to Bebermeier et al. [39], ancient settlements are covered by more than 7 m of alluvial and aeolian deposits. These formations of Mokattam (Qn2, Fig. 3b) and Maadi are repeatedly intercalated with fossils such as oysters, nummulites, and shale or sandy shale. Moreover, Bebermeier et al. [39] said that the fluvial sediments belonging to a former river system called prenile deposits (Qns, Fig. 3b) occupied the present-day Nile basin in the early Pleistocene. In the middle Pleistocene, the prenile deposited fluvial sediments (Qn2, Fig. 3b) east of the (Qns) deposits, closer to the present-day floodplain of the river Nile. These sediments (Qns and Qn2) were deposited directly on top of Eocene bedrock. Sahure's pyramid is located on the Nile silts (Qns), which reflects the geotechnical problems of the pyramid from the beginning of the construction due to the clay to claystone base (Fig. 3b).
a General geological map of the Memphis area and b a simplified geological map of the Abusir area. As shown in the legend, the pyramid is connected to the Mokattam formation and Maddi formation. Sahure's pyramid is located on Nile deposits/silt that was deposited directly to cover the Eocene bedrock. Edited after Ref. [39]
Generally, ancient Egyptians exploited approximately 200 quarries (Fig. 4) as sources of different kinds of stones, which were used as architectural, ornamental, and structural elements to build their temples, tombs, and pyramids from the predynastic era to the late Roman period, but limestone and sandstone were the dominant building materials for their buildings [40, 41]. In fact, most of the limestone blocks used by ancient Egyptians were brought from Tertiary formations, mainly Eocene, Paleocene, and Pliocene. In addition, some limestone building materials were from the Quaternary age. On the other hand, most of the sandstone blocks were prepared from Cretaceous Nubian formations [40,41,42]. Specifically, the stones and joint materials (mortars) of the pyramids are important and interesting to reveal much information related to ancient technology and their sustainability [25]. Pyramids were built from different kinds of stones, such as limestone, sandstone, sandy limestone, basalt, and granite. Cutting and preparation of stones from different quarries were an important process as the primary step for preparations of blocks of pyramids using different kinds of tools and techniques, such as using dolerite and crushed quartzite with sands in polishing of the stone surfaces [43] (Fig. 4).
Egypt is a country susceptible to climate change and geoenvironmental hazards such as sea-level rise, in addition to an increase in the intensity and frequency of temperature, wind (with sand and dust storms), heavy rains, and flash floods [48, 49]. Many geoenvironmental conditions affect the area of Abusir, especially temperature fluctuations, strong winds, and humidity. These environmental factors lead to physiochemical and mechanical damage to the structural materials and result in partial or total decay and collapse in some parts of the pyramids.
Air pollution is considered one of the environmental factors and challenges that affects the stones of Sahure's pyramid because it causes chemical weathering of the construction materials and thick black crust over the stone surfaces [54]. In Giza, it is noticed that from September to November, the number of pollutants decreases. On the other hand, in the season of wind, when the sky is strongly dark and strongly dark from March to May, the amount of pollutants increases, such as carbon monoxide, nitrogen oxides, ozone, and sulfur dioxide [55].
Intrinsic factors are defined as the internal problems of the construction materials, which are related to the chemical, physical and mechanical properties of the stones, and intrinsic problems are also related to the interaction between the environmental conditions and the intrinsic properties of the pyramid construction materials. Both intrinsic agents and geoenvironmental agents work together in pyramid stone decay. For example, gypsum salt is detected by means of chemical analysis in the weathered casing limestone of the pyramid due to the reaction between sulfate pollutants and carbonate to produce gypsum [56]. In this sense, and from in situ visual and macroscopic examinations, it is noticed that the fabric of stone is full of impurities and stained areas with yellowish spots, which reflects the weakness of the construction materials of the pyramid. 2ff7e9595c
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